1. Field of the Invention
The present invention relates to novel titanium dioxide sunscreen compositions.
2. Description of the Prior Art
Sunscreen compositions are commonly used during outdoor work or leisure for protection of exposed skin against painful sunburn. Many effective sunscreen preparations are sold commercially or are described in the cosmetic or pharmaceutical literature. In general, sunscreen preparations are formulated in the form of a cream, lotion or oil containing as the active agent an ultraviolet radiation absorbing chemical compound. The active agent acts to block the passage of erythematogenic radiation, thereby preventing its penetration into the skin.
The ideal sunscreen formulation should be nontoxic and non-irritating to skin tissue and be capable of convenient application to the skin in a uniform continuous film. The product should be sufficiently stable chemically and physically so as to provide an acceptable shelf life upon storage. It is particularly desirable that the preparation should retain its protective effect over a prolonged period after application. Thus, the active agent when present on the skin must be resistant to chemical or photo-degradation, to absorption through the skin and to removal by perspiration, skin oil or water. For aesthetic reasons, the product should be substantially odorless (or be capable of being scented) and be non-staining to the skin or clothing.
Microfine titanium dioxide has been found to be an effective sunscreen agent (U.S. Pat. Nos. 5,188,831 and 5,028,417; Japanese Patent Application No. 81-161,881; European Patent Application No. 91 30 40 98.6 published Nov. 13, 1991; Japanese Patent Publication No. 60-231,607; and British Journal of Dermatology, p. 275 (1971)) in that, when employed in cosmetic formulations in sufficiently small particle sizes, it is capable of transmitting visible light, but reflects and scatters harmful ultraviolet rays.
Relatively large amounts of microfine TiO.sub.2 can readily be incorporated into water-in-oil emulsions; however, such emulsions tend to feel greasier and are generally less acceptable cosmetically than oil-in-water emulsions. On the other hand, it has been difficult heretofore to form stable oil-in-water emulsions containing more than about 1%, by weight, of microfine TiO.sub.2. The presence of such low levels of microfine titanium dioxide does not increase the sunscreen protection.
It is an object of the present invention to provide stable oil-in-water emulsion compositions containing sufficiently large amounts of microfine TiO.sub.2 to increase sunscreen protection.